Wireless communication systems of various kinds are known in the art. These systems transmit signals at various frequencies or frequency ranges. A frequency range at which a wireless communication device may send a signal may be viewed as a channel. Certain wireless communication systems transmit primarily digital data. To do so, the digital data is usually converted into an analog signal that can be sent by a wireless transceiver. As part of the conversion or modulation, the transmission or signal obtains a particular spectral mask or characteristic response over the channel. The shape of the spectral mask is dependent on several factors including the type of modulation of the signal.
Wireless communication systems typically transmit data over a plurality of channels. To minimize interference between channels, the spectral mask of the transmissions should have spectral emissions, such as spurious emissions, below a certain level. Further, governmental bodies often regulate the frequency spectra available and the use of the frequencies by wireless communication system operators. These regulations may also restrict a transmission's emissions of the spectral mask at a given frequency or channel.
For example, the Federal Communications Commission (“FCC”) of the United States by regulation defines six blocks, each 5 MHz wide, of channels for Global System for Mobile communications (“GSM”) systems. The FCC regulations also include requirements that spectral emissions not exceed a certain level within a certain frequency range of a block edge. The spectral mask, however, for many wireless communication systems will have emissions that exceed this limitation. Other governmental bodies also impose spectral mask limitations on certain wireless communication transmissions.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.